John Jeschke has been yield mapping for nine years and has gained good information that he's used to enhance efficiencies. Yet he says yield mapping still has some serious soft spots. Other long-time yield mappers have had similar experiences resulting mostly in plusses, but also in a few problems.

Let's look at the positives first.

Jeschke, who raises corn and soybeans near Rock City, IL, uses yield maps to compare corn hybrids, soybean varieties and management practices across entire fields. “Full-field testing is much more valuable than doing strip tests,” he says.

“We compared corn after corn to corn after soybeans, and have seen 35- to 40-bu/acre better yields when corn was in rotation,” Jeschke reports. “We knew there was an advantage for rotation but didn't realize it was that great.”

Jeschke, who has long no-tilled soybeans, decided to compare no-till corn to corn grown with tillage. His yield monitor and maps showed no appreciable difference in yield between the two, and he now saves valuable dollars by no-tilling all his corn.

In Oakland, IA, Doug Applegate has been mapping yields for seven years. He's mapped planting data (to show which hybrids and which varieties are planted in each field) for six years. Applegate also uses yield maps to compare tillage practices.

“In comparing corn hybrids, we've found that good numbers tend to flip-flop from year to year as to which is better,” says Applegate. “But we see steady, predictable differences between the top hybrids and the poorer ones.”

Applegate, who primarily uses no-till, is using yield maps to compare no-till to deep ripping on river bottomland. He wants to look at several years of data before drawing conclusions.

George Ropp, an independent crop consultant in Van Wert, OH, works with farmer clients on yield mapping and analysis.

“One way we use the maps is to determine nutrient removal rates,” Ropp says. “That is, if particular areas in a field always yield about 175 bu/acre of corn, then we adjust the removal rate upward accordingly. Conversely, if there are areas that usually yield only about 100 bu/acre, we adjust the removal rate downward to that level. By matching the nutrient prescription to the various areas of the field, based on the yield maps, we make very efficient use of fertilizer dollars.”

Ropp says many of his clients have used the maps to show landlords the yield drop off in poorly drained areas. This has prompted some owners to install tiles.

“Our customers are using yield maps in fertilizer management and for more efficient weed control,” says Ron Waldschmidt of A.C. McCartney Co., Durand, IL. Waldschmidt, an AgLeader dealer, is on the Illinois-Wisconsin border.

“One customer overlays his soil sample map on his yield map for each field. He's applied manure to his fields over the years and has generally high nutrient levels. Where he has both high yields and ample fertility in a given area, he adjusts his fertilizer accordingly for a year.”

Another customer has observed a strong relationship between weed patches and yield reductions on his yield monitor during harvest and later on the yield maps. As a result, he's intensified weed control measures in those areas.

“This past year (2002) we had drought stress in our area,” says Waldschmidt. “Our farmers will use yield maps to see which varieties best tolerated that stress.”

From a holistic standpoint, yield monitor/mapping helps a grower understand the amount of yield variation that actually exists within a field, explains Tom Doerge, Pioneer agronomy research manager. This can lead to better site-specific management.

“Growers also can use yield maps as a feedback tool to help evaluate the performance of specific management inputs and decisions,” Doerge says.

Doerge says growers who have more time, interest and expertise will benefit the most from yield mapping. Unlike a commodity input such as Bt corn, in which every user gets the same benefit, yield mapping offers a payback that tends to be an individual thing.

Yet yield-mapping technology still has its warts.

“The biggest deficiency is in the software,” says Jeschke. “I don't expect the software to interpret the map, but it does need to correct such things as showing an ultra-high yield when the loaded combine is stopped. All the grain in the combine is attributed to that spot. This is especially a problem when the person who reads the map later is not the person who ran the combine and therefore doesn't know the situation.”

Applegate is also frustrated by the software.

“It's getting better but still has a long way to go,” he says. “For instance, it not only needs to take out the ‘bad’ data such as ‘loading up’ where the combine stops, but also on rolling ground where it ‘loads up’ yield at the bottom of the hills and vice-versa as you climb the hills.”

He adds, “At present, I'm able to compensate for the deficiencies because I run the combine — and can watch the monitor as I harvest — and I also read the maps. I know the ‘load up’ areas. When the day comes that somebody else is operating the combine and I'm reading the maps, I hope we have software that takes out the bad data.”

Monitor Matches Weigh Wagon

Pioneer Hi-Bred tests at 12 Illinois and Iowa locations in 2000 and 2001 showed that yield monitors are as accurate as weigh wagons in measuring corn yields. They gave strikingly similar results when ranking the yields of several hybrids or estimating yield differences between two hybrids.

Current Mapping Cost

The cost for the latest yield-mapping technology is less than $10,000, according to Ron Waldschmidt of A.C. McCartney Co., Durand, IL. An AgLeader system, including a yield monitor, GPS and software, is $8,485. A lightbar guidance system, which uses the same GPS gear, is an additional $1,500.